Copyright HBO (Six Feet Under)
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I have been watching Six Feet Under and the opening sequence includes a corvid. I thought it was a raven because it is much bigger than a normal crow and its feathers around the neck are shaggier, it also has a larger bill. So, I did some research and here is what I found out. It was a trick. It is indeed a crow but not an ordinary crow which is approximately 40–50 cm (16–20 inches) in length. It is being portrayed as an American Crow but it is reportedly a painted Pied Crow (Corvus Albus) which is often thought of as a small raven and is approximately 46–50 cm (18.1 - 23.6 inches) in length.
In the Season 1 commentary, the Director mentions that they used a Pied Crow which is native to Africa for the opening sequence and they painted it black to look like an American Crow instead of using an actual American Crow (Corvus brachyrhynchos) because it is illegal to film a crow in the United States under the Migratory Bird Treaty Act,

All native species of birds, with exception of upland game species (chukar, pheasant, quail, grouse), introduced species (starlings, house or "english sparrows", and feral pigeons) are protected by the MBTA. Migratory birds, their parts, nests or eggs may not be possessed, transported, imported, exported, purchased, sold, bartered, or offered for purchase, sale or barter without appropriate permits.

Use of birds for filming is not allowed in the United States, unless the film is produced for the purpose of wildlife conservation education (National Geographic or Discovery Channel films, for example). Commercial use of migratory birds is prohibited. This would include using birds in films produced for entertainment or commercials.

I guess we learn something new every day. The bird is beautiful but not right in it's natural state for the opening sequence, not dark enough, or so I imagine. And our ordinary American Crows are not film-able in the United States. Thus, we get a painted Pied Crow in the beginning of every episode of HBO's Six Feet Under. The ironic part of all this is... we are allowed to legally kill crows, just not film them for commercial purposes. Exploit them -- NO WAY! Kill them, sure. What strange laws we have.

Lane Jensen of Digital Kitchen wrote, "The thing we discovered about crows is that it is illegal to film true crows in the United States for commercial purposes. This crow was actually a pied crow. it has a white chest, so we painted the chest black. It was not very well trained, and it had to be on a leash, it didn't want to fly. "

Alan Poul from Six Feet Under wrote, "The thing that sticks out the most is the crow. Every effects house had come in with some kind of death-related imagery. But the crow seemed like something that was not so literally tied to the show and not overly macabre, but so evocative of the darker feelings the show would conjure up."